For the past eight years, Great Britain and the United States have been traveling parallel political paths under Margaret Thatcher and Ronald Reagan. Republicans are closely watching Thursday's British election for further clues to their best tactics in the 1988 elections. If Thatcher's Conservatives win their third term, you can expect the GOP to make her themes of growth, ownership and national pride as familiar as its own initials in 1988.
Republican National Chairman Frank J. Fahrenkopf Jr. went to London to observe last month's round of local elections and met with his Tory party counterpart, Norman Tebbit, the week that Thatcher decided to call a national election. At Tebbit's invitation, a Fahrenkopf aide has been sitting in on the final week of pre-election maneuvering.
The close cooperation is nothing new. In 1979, then-GOP chairman Bill Brock sent operatives to London to study the advertising themes and issues the Tories used to reclaim power. Strong echoes of the ''Labor Isn't Working'' theme turned up in Reagan's 1980 campaign, which weaned millions of working families, frustrated by stagflation, away from their normal Democratic loyalties.
Four years later, Fahrenkopf aides watched as Thatcher rode the euphoria and patriotic pride of her Falklands victory to an even more convincing second term. It was said at the time that Reagan had no comparable military credential. But then came Grenada, and suddenly the Republican admen proclaimed, ''America is back -- standing tall.''
This year again, the differences seem more striking than the similarities. The Conservatives have Thatcher at their head, and she is -- though controversial -- untainted by serious scandal. Republicans have a lame-duck president, damaged by the Iran-contra affair, and are uncertain who will lead them into the 1988 election.
Thatcher faces divided opposition, in Labor and the Liberal-Social Democratic Alliance, and the pre-election polls make her party the favorite to retain its parliamentary majority. Here, the Republicans no longer control either house of Congress, and the early surveys suggest (however shakily) that Democrats may hold the favorite's role for 1988.
''I'm not sure we can take comfort if she wins,'' Fahrenkopf remarked. ''But her campaign certainly is helpful in understanding how voters react to certain facts and certain appeals.''
The most important of those themes is economic growth without inflation. The Conservative manifesto (platform) says: ''Britain today is in the seventh successive year of steady economic growth. We have moved from the bottom to the top of the growth league of major European powers. . . . Since the Conservatives took office, productivity in British manufacturing has grown faster than in any other major industrialized country. . . .''
The same week the Tories' manifesto appeared, the Republican National Committee issued a ''special edition'' of one of its publications, asserting that, ''America is in the midst of a period of unparalleled economic progress and job growth. . . . We've created more than 13 million new jobs in this period. . . .''
Prosperity is a traditional boast of parties in power, and if the American economy remains healthy into 1988, you will certainly hear the Republicans taking credit for it. Of greater interest to the GOP is Thatcher's effort to redefine -- and realign -- the traditional class basis of British politics.
She has used every tool to make the average British family think of itself as owning a piece of the nation's future. Tories claim there are 2.5 million more home-owning families than in 1979, 1 million of them former public-housing tenants who were aided in buying the units they occupied. The number of individual stockholders has trebled, many of the new capitalists being employees of formerly nationalized industries now returned to private ownership.
Pre-election polls cited by The Economist, a British weekly, showed Tories winning among working-class voters who had joined the ranks of home-owners and stockholders. If those gains are confirmed on Thursday, you can expect to see a similar effort here, with GOP candidates arguing that the tax cuts and investment incentives of the Reagan years have given many more families ''a share in America.''
For all the current preoccupation in Washington with the Iran-contra hearings, history suggests that basic economic issues are likely to count more heavily at election time. Democrats, like Thatcher's opponents, assert that conservative policies have damaged the standing of the middle class. But if Thatcher wins the argument on her side of the Atlantic, the Republicans will gain important clues on how to win it here.